1. Field of the Invention
The present invention relates to a transmission rate control method for controlling transmission rate of an uplink user data, a mobile station, a radio base station, and a radio network controller.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional radio network controller RNC, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
In the “Enhanced Uplink”, a MAC-layer function, which is located in each cell of a radio base station Node B, is configured to control a transmission rate of uplink user data transmitted by a mobile station UE, using two transmission rate control channels described below.
As a first transmission rate control method, the MAC-layer function located in each cell of the radio base station Node B is configured to transmit an absolute value for a maximum allowable transmission rate of uplink user data (or parameter relating to the maximum allowable transmission rate) to each mobile station UE (individual mobile stations or all mobile stations) using an “Absolute Rate Grant Channel (AGCH)”, so as to control the transmission rate of uplink user data of each mobile station UE.
Here, the above-described parameter relating to the maximum allowable transmission rate is a transmission power ratio between an “Enhanced Dedicated Physical Data Channel (E-DPDCH)” and a “Dedicated Physical Control Channel (DPCCH)” (hereinafter, an EDCH transmission power ratio) or the like. This EDCH transmission power ratio is calculated by “transmission power of E-DPDCH/transmission power of DPCCH”.
The increase/decrease of the parameter relating to the maximum allowable transmission rate is corresponding to the increase/decrease of the transmission rate, and it is acquired in connection with the transmission rate. In 3GPP, this parameter relating to the maximum allowable transmission rate is defined as the EDCH transmission power ratio (See, Non-Patent literature 1:3GPP TSG-RAN TS25.309 v6.1.0).
As a second transmission rate control method, the MAC-layer function located in each cell of the radio base station Node B is configured to transmit a command indicating relative values such as an “Up Command”, a “Down Command”, a “Keep Command”, or the like, for a maximum allowable transmission rate of uplink user data (or parameter relating to the maximum allowable transmission rate) to each mobile station UE (individual mobile stations or all mobile stations) using a “Relative rate Grant Channel (RGCH)”, so as to control the transmission rate of uplink user data of each mobile station UE.
When the mobile station UE transmits uplink user data, the EDCH transmission power ratio which can be accepted by the mobile station UE (a maximum allowable EDCH transmission power ratio of mobile station UE) is determined using the above-mentioned transmission control channels (AGCH and RGCH).
Then, the mobile station UE determines a transmission data block size (TBS: Transport Block Size) per transmission time interval (TTI: Transmit Time Interval), based on the uplink user data size stored in a transmission buffer and the maximum allowable EDCH transmission power ratio of the mobile station UE.
Here, the mobile station UE is configured to determine the transmission data block size (TBS) per transmission time interval (TTI) using a correspondence table which shows correspondence between a transmission data block size (TBS) of uplink user data and the EDCH transmission power ratio.
As shown in Non-Patent literature 2 (3GPP TSG-RAN R2-042717), the radio network controller RNC is configured to notify the correspondence table to the mobile station UE by a layer-3 signaling, when a call setup is performed.
Also, the correspondence table can be set per upper layer flow to which a priority level, Quality of Service, or the like are set.
In the “Enhanced Uplink”, the mobile station UE is configured to transmit scheduling information (layer-2 control information) which includes the amount of data stored in a transmission buffer, conditions of transmission power, or the like, to the radio base station Node B, when the mobile station UE has the uplink user data to be transmitted, or the like.
The scheduling information can be configured to be transmitted together with the uplink user data in upper layer flow, or to be transmitted independently.
Referring to FIG. 3, an operation in the mobile station UE when uplink user data to be transmitted is occurred will be described.
As shown in FIG. 3, when the uplink user data to be transmitted is occurred in the mobile station UE, in step S1001, the mobile station UE transmits the scheduling information to the radio base station Node B, so as to request the transmission of uplink user data, in step S1002
In step S1003, the radio base station Node B transmits “Nack” to the mobile station UE, so as to request the retransmission of the uplink user data, when the radio base station Node B fails to perform the reception and decode processing towards the transmitted scheduling information.
In step S1004, the mobile station UE retransmits the scheduling information to the radio base station Node B.
When the radio base station Node B succeeds to perform the reception and decode processing towards the retransmitted scheduling information, in step S1005, the radio base station Node B transmits “Ack” to the mobile station UE. In addition, in step S1006, the radio base station Node B notifies the transmission rate of uplink user data (the EDCH transmission power ratio) to the mobile station UE using the rate control channel (AGCH and/or RGCH).
In step 1007, the mobile station UE determines the transmission data block size (TBS) of uplink user data based on the notified EDCH transmission power ratio, so as to transmit the uplink user data in upper layer flow using the determined transmission data block size (TBS).
In the example shown in FIG. 3, the radio base station Node B succeeded to perform the reception and decode processing toward the second scheduling information transmitted by the mobile station UE.
However, in order to shorten the transmission delay for uplink user data, the scheduling information is preferable to reach the radio base station Node B as soon as possible.
In a conventional mobile communication system using the “Enhanced Uplink”, “the correspondence table of the transmission data block size and the EDCH transmission power ratio”, which is used when transmitting the scheduling information independently, is not defined yet.
Accordingly, there has been a problem that the sufficient communication quality is not ensured, the retransmission of scheduling information is required often, and the long transmission delay is occurred.